Methods, well cement compositions and lightweight additives therefor

ABSTRACT

The present invention provides methods, lightweight well cement compositions and additives for the well cement compositions. The methods of the invention for sealing pipe in a well bore penetrating a zone or formation which readily fractures at low hydrostatic pressure is basically comprised of the steps of providing a lightweight cement composition comprised of a hydraulic cement, water and an additive comprising an aqueous suspension of microspheres containing a water swellable clay suspending agent, placing the cement composition in the annulus between the pipe and the well bore and allowing the cement composition to set.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation-in-part of application Ser.No. 10/005,266 filed on Dec. 3, 2001.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention.

[0003] The present invention relates to methods, compositions andlightweight additives for sealing pipe strings in well bores, and moreparticularly, to such methods, compositions and additives wherein thewell bores penetrate formations that readily fracture at low hydrostaticpressures.

[0004] 2. Description of the Prior Art.

[0005] Hydraulic cement compositions are commonly utilized in oil, gasand water well completion and remedial operations. For example,hydraulic cement compositions are used in primary cementing operationswhereby strings of pipe such as casing and liners are cemented in wellbores. In performing primary cementing, a hydraulic cement compositionis pumped into the annular space between the walls of a well bore andthe exterior of a string of pipe disposed therein. The cementcomposition is permitted to set in the annular space thereby forming anannular sheath of hardened substantially impermeable cement therein. Thecement sheath physically supports and positions the pipe in the wellbore and bonds the pipe to the walls of the well bore whereby theundesirable migration of fluids between zones or formations penetratedby the well bore is prevented.

[0006] In some well locations, the subterranean zones or formations intoor through which wells are drilled have high permeabilities and lowcompressive and tensile strengths. As a result, the resistance of thezones or formations to shear are low and they have low fracturegradients. When a hydraulic cement composition is introduced into a wellbore penetrating such a subterranean zone or formation, the hydrostaticpressure exerted on the walls of the well bore can exceed the fracturegradient of the zone or formation and cause fractures to be formed inthe zone or formation into which the cement composition is lost. Whilelightweight cement compositions have been developed and used,subterranean zones or formations are often encountered which havefracture gradients too low for the lightweight cement compositions to beutilized without the formation of fractures and the occurrence of lostcirculation problems.

[0007] Thus, there are needs for improved lightweight cementcompositions for sealing pipe such as casings and liners in well boreswhich penetrate zones or formations having very low fracture gradients.

SUMMARY OF THE INVENTION

[0008] The present invention provides lightweight well cementcompositions, additives for use in the compositions and methods of usingthe lightweight compositions for sealing pipe in well bores penetratingzones or formations having low fracture gradients which meet the needsdescribed above and overcome the deficiencies of the prior art. Themethods of this invention basically comprise the steps of providing alightweight cement composition comprised of a hydraulic cement, waterand an additive comprising a suspension of microspheres in water gelledor thickened with a water swellable clay suspending agent. The cementcomposition is placed into the annulus between a pipe and the walls of awell bore and the sealing composition is allowed to set into a hardimpermeable mass.

[0009] A lightweight sealing composition of this invention is basicallycomprised of a hydraulic cement, water and an additive for making thecement composition lightweight.

[0010] The additives of this invention are comprised of aqueoussuspensions of microspheres gelled or thickened with a water swellableclay suspending agent.

[0011] It is, therefore, a general object of the present invention toprovide methods, lightweight well cement compositions and additives foruse in cementing pipe in well bores.

[0012] Other and further objects, features and advantages of the presentinvention will be readily apparent to those skilled in the art upon areading of the description of preferred embodiments which follows.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0013] By the present invention, methods, lightweight well cementcompositions and additives therefor are provided for sealing pipes inwell bores penetrating zones or formations which readily fracture at lowhydrostatic pressures. The methods of this invention for sealing a pipein a well bore penetrating a zone or formation which readily fracturesat low hydrostatic pressures is basically comprised of providing alightweight cement composition comprised of a hydraulic cement, waterand an additive comprising a suspension of microspheres in water gelledor thickened with a water swellable clay suspending agent. Thelightweight cement composition is placed into the annulus between theexterior surfaces of the pipe and the walls of the well bore and thecement composition is allowed to set into a hard impermeable masstherein.

[0014] A variety of hydraulic cements can be utilized in accordance withthe present invention including those comprised of calcium, aluminum,silicon, oxygen and/or sulfur which set and harden by reaction withwater. Such hydraulic cements include Portland cements, slag cements,pozzolana cements, gypsum cements, aluminous cements and silica cements.Portland cements or their equivalents are generally preferred for use inaccordance with the present invention. Portland cements of the typesdefined and described in the API Specification For Materials And TestingFor Well Cements, API Specification 10, 5^(th) Edition, dated Jul. 1,1990 of the American Petroleum Institute are particularly suitable.Preferred API Portland cements include Classes A, B, C, G and H withClasses G and H being more preferred, and Class G being the mostpreferred.

[0015] The mix water utilized to form the cement compositions of thisinvention can be fresh water, unsaturated salt solutions or saturatedsalt solutions. The water is included in the cement compositions of thisinvention in an amount in the range of from about 60% to about 250% byweight of hydraulic cement therein.

[0016] The additive which is included in the cement compositions of thisinvention to make the compositions lightweight is basically comprised ofa suspension of microspheres in water gelled or thickened with a waterswellable clay suspending agent. While various microspheres can beutilized, fly ash microspheres are preferred for use in the presentinvention. Particularly suitable such fly ash microspheres arecommercially available from Halliburton Energy Services, Inc. of Duncan,Oklahoma under the tradename “SPHERELITE™”. Another type of microspheresthat can be used is synthetic hollow glass microspheres commerciallyavailable from Minnesota Mining and Manufacturing Company (3M™) underthe tradename “SCOTCHLITE™”. These very low density microspheres areformed of a chemically stable soda-lime borosilicate glass compositionwhich is non-porous. The microspheres used are included in the aqueousmicrosphere suspension in a general amount in the range of from about30% to about 100% by weight of water in the suspension. Preferably, themicrospheres are included in the suspension in an amount of about 67% byweight of water therein.

[0017] The water swellable clay suspending agents which can be usedinclude, but are not limited to sodium bentonite, attapulgite, kalonite,meta kalonite, hectorite or sepiolite. Of these, sodium bentonite ispreferred. The clay suspending agent used is included in the aqueoussuspension in an amount in the range of from about 1% to about 4% byweight of the water therein, preferably an amount of about 2% by weightof the water therein.

[0018] The lightweight additive is included in the cement composition inan amount in the range of from about 30% to about 100% by weight ofhydraulic cement therein.

[0019] As will be understood by those skilled in the art, variousconventional additives can be included in the lightweight sealingcompositions of this invention including, but not limited to, setretarders, set accelerators, fluid loss control additives anddispersants.

[0020] A preferred method of this invention for sealing pipe in a wellbore penetrating a zone or formation which readily fractures at lowhydrostatic pressures is comprised of the steps of: (a) providing alightweight cement composition comprised of a hydraulic cement, mixwater and an additive comprising an aqueous suspension of microspherescontaining a water swellable clay suspending agent; (b) placing thecement composition between the exterior surfaces of the pipe and thewalls of the well bore; and (c) allowing the cement composition to setinto a hard impermeable mass.

[0021] A more preferred method of the present invention for sealing pipein a well bore penetrating a zone or formation which readily fracturesat low hydrostatic pressures is comprised of the steps of: (a) providinga lightweight cement composition comprised of a hydraulic cement, mixwater present in the composition in an amount in the range of from about60% to about 250% by weight of the hydraulic cement therein and anadditive comprising an aqueous suspension of microspheres containingwater, fly ash microspheres and a sodium bentonite suspending agentpresent in the cement composition in an amount in the range of fromabout 30% to about 100% by weight of hydraulic cement therein; (b)placing the cement composition into the annulus between the pipe and thewalls of the well bore; and (c) allowing the cement composition to setinto a hard impermeable mass.

[0022] A preferred lightweight well cement composition of this inventionis comprised of: a hydraulic cement; mix water selected from the groupof fresh water, unsaturated salt solutions and saturated salt solutionspresent in an amount in the range of from about 60% to about 250% byweight of the hydraulic cement in the composition; and an additivecomprised of an aqueous suspension of microspheres containing water,microspheres and a sodium bentonite suspending agent present in anamount in the range of from about 30% to about 100% by weight ofhydraulic cement in the composition.

[0023] A preferred lightweight cement composition additive of thisinvention is comprised of an aqueous suspension of microspherescontaining water, microspheres and a sodium bentonite suspending agent.

[0024] A more preferred lightweight cement composition additive of thisinvention is comprised of: an aqueous suspension of fly ash microspherescontaining water, fly ash microspheres and a sodium bentonite suspendingagent, the fly ash microspheres being present in an amount in the rangeof from about 30% to about 100% by weight of water in the additive; andthe sodium bentonite suspending agent being present in an amount in therange of from about 1% to about 4% by weight of water in the additive.

[0025] The most preferred lightweight cement composition additive ofthis invention is comprised of: an aqueous suspension of fly ashmicrospheres containing water, fly ash microspheres and a sodiumbentonite suspending agent, the fly ash microspheres being present in anamount of about 67% by weight of water in the additive; and the sodiumbentonite being present in an amount of about 2% by weight of water inthe additive.

[0026] In order to further illustrate the methods, the lightweight wellcement compositions and the additives of this present invention, thefollowing examples are given.

EXAMPLE

[0027] A lightweight additive of this invention was prepared byhydrating 20 grams of sodium bentonite in 1000 grams of water. To 600grams of the resulting water gelled with sodium bentonite, 400 grams offly ash microspheres were added. 300 grams of Portland cement were thenmixed with 300 grams of the lightweight additive and 150 grams of freshwater. The resulting cement slurry was subjected to 4000 psi of pressureto simulate the hydraulic pressure at the bottom of a well bore. Afterbeing subjected to the applied pressure, the density of the slurry was11.2 lb/gal. The slurry was poured into a plexiglass tube measuring 12inches in length and 1.75 inches internal diameter. The slurry was thenallowed to set to form a hardened mass after which a one inch sectionwas cut from the top and bottom of the plexiglass tube. The hardenedcement was removed from the one inch sections of the tube and theirdensities determined. The density of the bottom section was 11.1 lb/galand the density of the top section was 11.3 lb/gal. This shows that,within experimental error, the cement was uniform in density and theexperimental liquid additive was effective in preparing a lightweightcement.

[0028] Thus, the present invention is well adapted to carry out theobjects and attain the ends and advantages mentioned as well as thosewhich are inherent therein. While numerous changes may be made by thoseskilled in the art, such changes are encompassed within the spirit ofthis invention as defined by the appended claims.

What is claimed is:
 1. A method of sealing pipe in a well borepenetrating a zone or formation which readily fractures at lowhydrostatic pressures comprising the steps of: (a) providing alightweight cement composition comprised of a hydraulic cement, mixwater and an additive comprising an aqueous suspension of microspherescontaining a water swellable clay suspending agent; (b) placing saidcement composition between the exterior surfaces of said pipe and thewalls of said well bore; and (c) allowing said cement composition to setinto a hard impermeable mass.
 2. The method of claim 1 wherein saidhydraulic cement in said composition is selected from the group ofPortland cements, slag cements, pozzolana cements, gypsum cements,aluminous cements and silica cements.
 3. The method of claim 1 whereinsaid hydraulic cement is Portland cement.
 4. The method of claim 1wherein said mix water is selected from the group consisting of freshwater, unsaturated salt solutions and saturated salt solutions.
 5. Themethod of claim 1 wherein said water is present in said cementcomposition in an amount in the range of from about 60% to about 250% byweight of hydraulic cement therein.
 6. The method of claim 1 whereinsaid additive is present in said composition in an amount in the rangeof from about 30% to about 100% by weight of hydraulic cement therein.7. The method of claim 1 wherein said microspheres are fly ashmicrospheres.
 8. The method of claim 1 wherein said microspheres arepresent in said additive in an amount in the range of from about 30% toabout 100% by weight of water in said additive.
 9. The method of claim 1wherein said clay suspending agent is selected from the group consistingof sodium bentonite, attapulgite, kalonite, meta kalonite, hectorite andsepiolite.
 10. The method of claim 1 wherein said clay suspending agentis sodium bentonite. 11 The method of claim 1 wherein said claysuspending agent is present in said additive in an amount in the rangeof from about 1% to about 4% by weight of water in said additive.
 12. Alightweight well cement composition comprised of: a hydraulic cement;mix water; and an additive comprised of an aqueous suspension ofmicrospheres containing water, microspheres and a water swellable claysuspending agent.
 13. The composition of claim 12 wherein said hydrauliccement is selected from the group of Portland cements, slag cements,pozzolana cements, gypsum cements, aluminous cements and silica cements.14. The composition of claim 12 wherein said hydraulic cement isPortland cement.
 15. The composition of claim 12 wherein said mix wateris selected from the group consisting of fresh water, unsaturated saltsolutions and saturated salt solutions.
 16. The composition of claim 12wherein said mix water is present in an amount in the range of fromabout 60% to about 250% by weight of hydraulic cement therein.
 17. Thecomposition of claim 12 wherein said additive is present in an amount inthe range of from about 30% to about 100% by weight of hydraulic cementtherein.
 18. The composition of claim 12 wherein said microspheres arefly ash microspheres.
 19. The composition of claim 12 wherein saidmicrospheres are present in said additive in an amount in the range offrom about 30% to about 100% by weight of water in said additive. 20.The composition of claim 12 wherein said clay suspending agent isselected from the group consisting of sodium bentonite, attapulgite,kalonite, meta kalonite, hectorite and sepiolite.
 21. The composition ofclaim 12 wherein said clay suspending agent is sodium bentonite.
 22. Thecomposition of claim 12 wherein said clay suspending agent is present insaid additive in an amount in the range of from about 1% to about 4% byweight of water in said additive.
 23. A lightweight cement compositionadditive comprised of an aqueous suspension of microspheres containingwater, microspheres and a water swellable clay suspending agent.
 24. Theadditive of claim 23 wherein said microspheres are fly ash microspheres.25. The additive of claim 23 wherein said microspheres are present in anamount in the range of from about 30% to about 100% by weight of waterin said additive.
 26. The additive of claim 23 wherein said claysuspending agent is selected from the group consisting of sodiumbentonite, attapulgite, kalonite, meta kalonite, hectorite andsepiolite.
 27. The additive of claim 23 wherein said clay suspendingagent is sodium bentonite.
 28. The additive of claim 23 wherein saidclay suspending agent is present in an amount in the range of from about1% to about 4% by weight of water in said additive.
 29. The additive ofclaim 23 wherein said microspheres are present in an amount of about 67%by weight of water in said additive.
 30. The additive of claim 27wherein said sodium bentonite is present in an of about 2% by weight ofwater in said additive.